The present invention relates to a method of applying opaque coatings on electronic devices. Essentially, the process comprises selectively depositing compositions comprising silica precursor resins and opaque fillers. The resultant coatings provide both an environmental barrier for the device and a mechanism which inhibits inspection and reverse engineering of the device.
The use of silica-containing ceramic coatings on substrates such as electronic devices is known in the art. For instance, Haluska et al. in U.S. Pat. Nos. 4,749,631 and 4,756,977 disclose processes for forming silica coatings on electronic substrates wherein solutions of silica precursor resins are applied to substrates followed by heating the coated substrates in air at a temperature in the range of 200.degree.-1000.degree. C. These references, however, do not describe the use of fillers within the coating nor the selective deposition process claimed herein.
Similarly, the use of opaque fillers within ceramic coatings for electronic devices is also known in the art. For instance, U.S. Pat. No. 5,258,334 describes a composition comprising a silica precursor resin and a filler which is used to coat the surface of an electronic device. It is taught therein that the silica precursor is applied or flows over the surface of the device to deny visual access. Since the resultant coating is opaque, however, it is difficult to etch at the bond pads and streets for interconnection and dicing.
The object of the present invention is to develop an efficient method for depositing opaque coatings on electronic devices. The present inventors have now discovered such a process in which ceramic coatings derived from compositions comprising silica precursor resins and fillers are selectively applied to the surface of the device.